Photolithography is commonly used during formation of integrated circuits on semiconductor wafers. More specifically, a form of radiant energy (such as, for example, ultraviolet light) is passed through a radiation patterning tool and onto a semiconductor wafer. The radiation patterning tool can be, for example, a photomask or a reticle, with the term “photomask” traditionally being understood to refer to masks which define a pattern for an entirety of a wafer, and the term “reticle” traditionally being understood to refer to a patterning tool which defines a pattern for only a portion of a wafer. However, the terms “photomask” (or more generally “mask”) and “reticle” are frequently used interchangeably in modern parlance, so that either term can refer to a radiation patterning tool that encompasses either a portion or an entirety of a wafer.
Radiation patterning tools contain light restrictive regions (for example, totally opaque or attenuated/half-toned regions) and light transmissive regions (for example, totally transparent regions) formed in a desired pattern. A grating pattern, for example, can be used to define parallel-spaced conductive lines on a semiconductor wafer. The wafer is provided with a layer of photosensitive resist material commonly referred to as photoresist. Radiation passes through the radiation patterning tool onto the layer of photoresist and transfers the mask pattern to the photoresist. The photoresist is then developed to remove either the exposed portions of photoresist for a positive photoresist or the unexposed portions of the photoresist for a negative photoresist. The remaining patterned photoresist can then be used as a mask on the wafer during a subsequent semiconductor fabrication step, such as, for example, ion implantation or etching relative to materials on the wafer proximate the photoresist.
Advances in semiconductor integrated circuit performance have typically been accompanied by a simultaneous decrease in integrated circuit device dimensions and a decrease in the dimensions of conductor elements which connect those integrated circuit devices. The demand for ever smaller integrated circuit devices brings with it demands for ever-decreasing dimensions of structural elements, and ever-increasing requirements for precision and accuracy in radiation patterning with reticles and photomasks.
A pattern which is frequently desired to be imparted to photoresist is a circle, and it can be particularly desired to form circles having diameters on the order of microns, and even more desired to form circles having diameters on the order of sub-microns. The circle can have numerous applications in forming semiconductor circuitry, such as, for example, applications in forming cylindrical openings. Difficulties exist in fabricating reticles which can pattern circles having diameters on the order of microns and sub-microns. Typically, ovals are patterned instead of the desired circles, which can cause more semiconductor real estate to be consumed than would be utilized if circles could be generated. It would be desirable to develop radiation patterning tools which could pattern circular shapes at the micron and sub-micron level, or at least generate more substantially circular shapes than are produced by present methods.
Other shapes, besides circular shapes, can be desired in various semiconductor processes. It is generally desired to accurately print the desired shapes, but such is frequently difficult. If a shape is not accurately printed, it can overlap in regions where it is not desired, and ultimately lead to circuit shorts, or other undesired problems. It is therefore desired to develop photolithographic methods and devices which can be utilized to accurately print desired shapes.